This disclosure relates to an engine system of a motor vehicle including an engine having at least two camshafts driven by an endless drive from a crankshaft of the engine and in particular to adaptively controlling the engine based upon variations in camshaft timing due to wear of the endless drive.
It is known that over time an endless drive used to drive a pair of camshafts of an engine will wear due to usage and that this wear has the effect of producing elongation of the endless drive (primary drive) and includes both stretching of the endless drive itself and abrasion of parts of the endless drive such as the teeth of a toothed belt and the links of a drive chain.
Such wear will result in the angular relationship between the crankshaft and the camshafts and between the two camshafts changing thereby resulting in valve timing errors.
Primary drive elongation will cause a shift in the retarded direction for both the intake and exhaust camshaft timing and this in turn will degrade combustion stability and fuel economy at idle and other part-load conditions and will reduce volumetric efficiency at high loads thereby reducing available torque from the engine.
In addition, retarded exhaust camshaft timing will erode any safety margin that protects against piston to valve contact and retarded intake camshaft timing will reduce the available window for safe operation of valve deactivation required for cylinder deactivation.
In addition to the foregoing, any primary drive tensioner provided to remove the additional primary drive slack caused by primary drive elongation will only function effectively up to a predetermined percentage elongation of the primary drive.
It is an object of this disclosure to provide a method of controlling an engine system of a motor vehicle including an engine having at least two camshafts driven by an endless drive from a crankshaft of the engine including an endless drive evaluation process to confirm and quantify the presence of endless drive elongation and the adaptive control of the engine based upon the results of the endless drive evaluation process.
According to a first aspect of the disclosure there is provided a method of adaptively controlling a motor vehicle engine system comprising an engine having a crankshaft, first and second camshafts driven by an endless drive system including an endless drive from a crankshaft of the engine and an electronic controller wherein the method comprises: measuring an angular position for one of the first and second camshafts when the crankshaft is in a reference position and using the measured angular position to produce a value of change in angular position for the one camshaft; measuring an angular position for the other camshaft of the first and second camshafts when the crankshaft is the same reference position and using the measured angular position to produce a value of change in angular position for the other camshaft; establishing whether any change in angular position for one camshaft is in the same retarded direction as a corresponding angular change for the other camshaft; establishing whether any changes in angular position of the camshafts are gradual changes; establishing whether a ratio of change of angular position of one camshaft with respect to the other camshaft is substantially equal to a predefined fixed ratio based upon the geometry of the endless drive system; and if the results of steps c to e indicate that any change in angular position is in the same retarded direction for both camshafts and any changes in angular position are gradual changes and the ratio of angular change of one camshaft with respect to the other camshaft is substantially equal to a predefined fixed ratio based upon the geometry of the endless drive system, the method further comprises confirming that the current change in angular position of the first and second camshafts is the result of elongation of the endless drive and using the measured angular positions of the first and second camshafts in the control of one or more operational functions of the engine.
This has the advantage that not only can elongation of the endless drive be detected it can also be confirmed that any changes in angular position of the camshafts are due to such elongation and not to some other system error or fault.
Establishing whether any change in angular position for one camshaft is in the same retarded direction as a corresponding angular change for the other camshaft may comprise measuring the angular position of the first and second camshafts when the crankshaft is in the reference position, comparing the current measured angular positions of the first and second camshafts with previously saved datum angular positions for the first and second camshafts to quantify the difference in angular position of each camshaft compared to its respective datum position and using the differences in angular position to establish whether the changes in angular position are in the same retarded direction for both camshafts.
Establishing whether any changes in angular position of the camshafts are a gradual changes may comprise comparing the current measured position of each camshaft when the crankshaft is in a reference position with one or more preceding measurements of angular position for the same camshaft when the crankshaft is in the same reference position and if the changes in angular position follow a substantially uniform pattern using this as confirmation that the changes in angular position are the result of gradual elongation of the endless drive.
Establishing whether a ratio of change of angular position of one of the camshafts compared to the other camshaft is substantially equal to a predefined fixed ratio based upon the geometry of the endless drive system may comprise dividing a change in angular position of one of the camshafts with a corresponding change in angular position of the other camshaft to produce a calculated ratio of change and comparing the calculated ratio of change with a predefined ratio based upon the geometry of the endless drive system.
The operational function of the engine may be the timing of the opening and closing of exhaust valves of the engine to meet a current demand.
The operational function of the engine may be the timing of the opening and closing of inlet valves of the engine to meet a current demand.
The operational function of the engine may be the closing of an exhaust valve of a cylinder of the engine to avoid contact between the respective valve and a piston of the respective cylinder.
The engine may have a deactivatable cylinder and the operational function of the engine may be the deactivation of the deactivatable cylinder of the engine.
The first camshaft may be an inlet camshaft and the measured angular position of the inlet camshaft of the engine may be used to adapt a deactivation control window for the deactivatable cylinder of the engine.
The operational function may be the provision of an indication to a user of the motor vehicle that a predefined action is advised when the measured angular positions of the first and second camshafts indicate that a predefined elongation limit for the endless drive has been exceeded.
The predefined action may be one of changing the oil of the engine and changing the endless drive of the engine.
The first camshaft may be an inlet camshaft and the second camshaft may be an exhaust camshaft.
The endless drive system may comprise a chain engaged with a driving chain wheel attached to the crankshaft of the engine and first and second driven chain wheels fastened to the first and second camshafts respectively.
According to a second aspect of the disclosure there is provided a motor vehicle engine system comprising an engine having first and second camshafts driven by an endless drive system including an endless drive from a crankshaft of the engine, a crankshaft sensor to sense the rotational position of the crankshaft and first and second camshaft sensors to sense the rotational positions of the first and second camshafts respectively when the crankshaft is in a reference position and an electronic controller to process outputs from the crankshaft sensor and the two camshaft sensors wherein the electronic controller is operable to: use the outputs from the first and second camshaft sensors to establish whether any change in angular position for one camshaft is in the same retarded direction as a corresponding angular change for the other camshaft; use the outputs from the first and second camshaft sensors to establish whether any changes in angular position of the camshafts are gradual changes; use the outputs from the first and second camshaft sensors to establish whether a ratio of change of angular position of one camshaft with respect to the other camshaft is substantially equal to a predefined fixed ratio based upon the geometry of the endless drive system; and if the results of steps a to c indicate that any change in angular position is in the same retarded direction for both camshafts and any changes in angular position are gradual changes and the ratio of angular change of one camshaft with respect to the other camshaft is substantially equal to a predefined fixed ratio based upon the geometry of the endless drive system, the electronic controller is operable to use this as confirmation that a current change in angular position of the first and second camshafts is the result of elongation of the endless drive and is further operable to use the measured angular positions of the first and second camshafts in the control of one or more operational functions of the engine.
The electronic controller may be operable to establish whether any change in angular position for one camshaft is in the same retarded direction as a corresponding angular change for the other camshaft by using the first and second camshaft sensors to measure the angular position of the first and second camshafts when the crankshaft is sensed by the crankshaft sensor to be in the reference position, compare the current measured angular positions of the first and second camshafts with datum angular positions for the first and second camshafts previously saved in a memory of the electronic controller to quantify the difference in angular position of each camshaft compared to its respective datum position and use the differences in angular position to establish whether the changes in angular position are in the same retarded direction for both camshafts.
The electronic controller may be arranged to establish whether any changes in angular position of the camshafts are a gradual changes by comparing the current measured position of each camshaft as provided by the outputs from the first and second camshaft sensors when the crankshaft is sensed by the crankshaft sensor to be in the reference position with one or more preceding measurements of angular position for the same camshaft when the crankshaft is in the same reference position and, if the changes in angular position follow a substantially uniform pattern, confirm that the changes in angular position are the result of gradual elongation of the endless drive.
The electronic controller may be arranged to establish whether the ratio of change of angular position of one of the camshafts compared to the other camshaft is substantially equal to a predefined fixed ratio based upon the geometry of the endless drive system by dividing a change in angular position of one of the camshafts with a corresponding change in angular position of the other camshaft to produce a calculated ratio of change and comparing the calculated ratio of change with a predefined ratio stored in a memory of the electronic controller based upon the geometry of the endless drive system.
The predefined ratio may be a ratio of the length of the endless drive from a drive wheel attached to the crankshaft to a driven wheel attached to one end of the first camshaft with respect to the sum of the length of the endless drive from the drive wheel attached to the crankshaft to the driven wheel attached to one end of the first camshaft and the length of the endless drive between the driven wheel attached to the first camshaft and a driven wheel attached to one end of the second camshaft.
The operational function of the engine may be the timing of the opening and closing of exhaust valves of the engine to meet a current demand.
The operational function of the engine may be the timing of the opening and closing of inlet valves of the engine to meet a current demand.
The operational function of the engine may be the closing of an exhaust valve of a cylinder of the engine to avoid contact between the respective valve and a piston of the respective cylinder.
The engine may have a deactivatable cylinder and the operational function of the engine may be the deactivation by the electronic controller of the deactivatable cylinder of the engine.
The first camshaft may be an inlet camshaft and the measured angular position of the inlet camshaft of the engine may be used to adapt a deactivation control window associated with the deactivatable cylinder of the engine and the electronic controller is arranged to prevent deactivation of the deactivatable cylinder if the current inlet camshaft position is outside the deactivation window.
The operational function may be the provision by the electronic controller of an indication to a user of the motor vehicle that a predefined action is advised when the measured angular positions of the first and second camshafts indicate that a predefined elongation limit for the endless drive has been exceeded.
The predefined action may be one of changing the oil of the engine and changing the endless drive of the engine.
The first camshaft may be an inlet camshaft of the engine and the second camshaft may be an exhaust camshaft of the engine.
According to a third aspect of the disclosure there is provided a motor vehicle having an engine system constructed in accordance with said second aspect of the disclosure.